Vehicle seat systems include various functional mechanisms. In seat design, there is a need for an improved seat height adjustment guiding mechanism and to a seat rotation adjustment guiding mechanism that prevent any wobble and shaking motion during operational use.
U.S. Pat. No. 5,374,102 describes a seat height adjustment guiding mechanism including three screw adjustment mechanisms with Belleville washers that are configured to tighten in close contact one sliding cylindrical part with a second stationary cylindrical part while restricting rotation motion. The document does not appear to clearly explain which component of the mechanism is configured to absorb any mechanism part dimensional variation in order to be able to provide free space when a maintenance person will tighten screws more to keep a good contact with the sliding cylindrical part.
More precisely, U.S. Pat. No. 5,374,102 describes three identical vertically oriented bars which keep roller bearings in position. Typically during the assembly of the mechanism, the two first vertically oriented bar being screwed would inherently be screwed until contact is made between the vertically oriented bar and the stationary cylindrical part in which the roller bearings are contained or between the two cylindrical parts in opposite location with respect to the location where the roller bearing is applying load between the two cylindrical parts. This last solution results in too much friction to enable smooth linear motion guiding and requires re-adjustment between the three vertically oriented bars. In the first solution, which is certainly the best, the role of each of the three vertically oriented bars is not identical and therefore it is not obvious for a maintenance person to determine which bolt should be tightened more.
Assembly of the above mechanism has to include an iterative tightening of the six screws slightly one after the other until the proper compression is achieved. However, it would be desirable if this solution could be avoided.
One important function of such a guiding mechanism is to restrict rotation between the two cylindrical parts. The document does not appear to clearly explain which component of the mechanism is configured to absorb the rotation load applied on the sliding cylindrical part which is transmitted on the roller bearings. This rotation load between the two cylindrical parts is transformed in two force components on each roller bearing. The first component is a friction force parallel to the rolling surface of the bearing and the other one is perpendicular to the rolling surface of the bearing. This last perpendicular force is not centered on the roller bearing thickness depending on which direction the rotation load and therefore the screws of the floating vertically oriented bar will experience flexion forces.
Moreover, the screws of the floating vertically oriented bar are softly pre-loaded in order to allow roller bearings to still roll. These conditions give screws that are not pre-loaded enough to ensure a good fatigue resistance in particular to flexion forces. In the presence of dynamic and cycling stresses, the screws are at risk of sudden failure.
Finally, U.S. Pat. No. 5,374,102 does not provide a means to ensure that adjustment will not change over time with vibration and stresses, especially on the screws of the floating vertically oriented bar which are not fully pre-loaded.
U.S. Pat. No. 4,705,256 describes a seat swivel adjustment guiding mechanism which uses a well-known central bolt pivot with an addition of at least one bearing clamp in order to secure the mechanism and to transfer a portion of the off centered loads of the swivel plate directly to the stationary frame under. Typically the central bolt pivot is welded in position to reduce the risk of loosening. This system must occupy the central area of the seat mechanism where the pivot bolt is located. In the same manner, U.S. Pat. No. 4,948,086A describes a rotating guide with bearing acetal plate and coil spring to exert compressive force on the sliding assembly. This device has a screw system also occupying the central area of the seat.
U.S. Pat. No. 6,447,065B1 describes a load clamping mechanism, which clears the central area of the device, and is configured to adjust the pressure exerted on bearings to vary the rotating force needed for rotation of the swivel system.
U.S. Pat. No. 5,374,102 also describes a seat swivel adjustment guiding mechanism with a free central portion which is occupied with a cylinder with its handle for powering and activating the height adjustment. The guiding is done with interaction of two concentrically cylindrical tubes. In this condition however, it is difficult to control in an adjustable way the mechanical free play to prevent wobbling and shaking motion.
There is thus a need for a seat adjustment system, which by virtue of its design and components would be able to overcome or at least minimize at least one of the above-mentioned drawbacks.